(A customer approaches the counter with curtains in her hand. Her 15-year-old daughter hovers around.)

Me: “Hello, ma’am! Those curtains will be a total of $45, at $15 a piece.”

Customer: “What? No, the sign said $5 a piece.”

Me: “Really? I’m very sorry for the inconvenience, ma’am; I was told not to sell these specific curtains for any less than $15. We are a charity drive, so I hope you understand the pricing.”

Customer: “No, you don’t get it. These curtains were over there on that rack, and it said $5! You are bound, by law, to sell me these at this pri—”

(The daughter interrupts.)

Customer’s Daughter: “Actually, she’s not. The sign beside the curtains could have been referring to any number of things. That said, even if we were to assume that it referred to the curtains themselves, it would only constitute an invitation to treat, which is something very different to an offer. You know as well as I do that both an offer and an acceptance are needed to form a contract. By taking the curtains to the counter, you’re offering, and by disagreeing with an express term of the contract—in this case, the price—this lovely lady who’s merely performing her job is not accepting. Therefore, no contract has been formed.”

Customer: “I… I… shut up!”

(The customer storms out of the shop.)

Me: “Thank you!”

Customer’s Daughter: “No problem. I just finished a semester on contract law, and she’s done this in the past three stores we’ve gone to. I hope things look up for you!”